1. Field of the Invention
The present invention relates to golf balls. Specifically, the present invention relates to golf balls that include a solid core, a mid layer, and a cover.
2. Description of the Related Art
Golf players' foremost requirement for golf balls is flight performance. Golf players place importance on flight performance upon shots with a driver, a long iron, and a middle iron. Flight performance correlates with the resilience performance of a golf ball. When a golf ball having excellent resilience performance is hit, the golf ball flies at a high speed, thereby achieving a large flight distance.
An appropriate trajectory height is required in order to achieve a large flight distance. A trajectory height depends on a spin rate and a launch angle. In a golf ball that achieves a high trajectory by a high spin rate, a flight distance is insufficient. In a golf ball that achieves a high trajectory by a high launch angle, a large flight distance is obtained. An outer-hard/inner-soft structure in a golf ball can achieve a low spin rate and a high launch angle.
Golf players also place importance on spin performance of golf balls. When a backspin rate is high, the run is short. It is easy for golf players to cause a golf ball, to which backspin is easily provided, to stop at a target point. When a sidespin rate is high, the golf ball tends to curve. It is easy for golf players to intentionally cause a golf ball, to which sidespin is easily provided, to curve. A golf ball to which spin is easily provided has excellent controllability. In particular, advanced golf players place importance on controllability upon a shot with a short iron.
JPH2-264674 (U.S. Pat. No. 5,072,944) discloses a golf ball that includes a core consisting of a center core and an outer layer. The center core is flexible, and the outer layer is hard. The core suppresses a spin rate.
JPH6-98949 (U.S. Pat. No. 5,516,110) discloses a golf ball having a constant hardness between: a point that is located at a distance of 5 mm from a central point; and a point that is located at a distance of 10 mm from the central point. A similar golf ball is also disclosed in JPH6-154357 (U.S. Pat. No. 5,403,010).
JPH7-112036 (U.S. Pat. No. 5,562,287) discloses a golf ball having a small difference between a central hardness and a surface hardness of a core. The core contributes to the resilience performance of the golf ball.
JP2002-765 (US 2002/0019269) discloses a golf ball having a great difference between a central hardness and a surface hardness of a core.
JP2003-33447 (US 2003/0032501) discloses a golf ball that includes a core for which a rubber composition includes a polysulfide. The polysulfide contributes to the resilience performance of the golf ball.
JP2008-194473 (US 2008/0194357 and US 2008/0312008) discloses a golf ball having a great difference between a central hardness and a surface hardness of a core. A similar golf ball is also disclosed in JP2010-22504.
In the golf ball disclosed in JPH2-264674, the structure of the core is complicated. The core produces an energy loss when being hit. In addition, the core has inferior durability.
In the golf ball disclosed in JPH6-98949, a range where the hardness is constant is narrow. The golf ball has inferior resilience performance. Similarly, the golf ball disclosed in JPH6-154357 also has inferior resilience performance.
In the golf ball disclosed in JPH7-112036, a spin rate is excessive. The golf ball has a small flight distance.
The golf ball disclosed in JP2002-765 has inferior resilience performance.
In the golf ball disclosed in JP2003-33447, a spin rate is excessive. The golf ball has inferior flight performance.
In the golf ball disclosed in JP2008-194473, there is a zone in which a hardness decreases from the central point of the core toward the surface of the core. The golf ball has inferior resilience performance. In the golf ball, a spin rate is excessive. The golf ball has inferior flight performance. Similarly, the golf ball disclosed in JP2010-22504 also has inferior flight performance.
An object of the present invention is to provide a golf ball having excellent flight performance.